Migratory and dispersive. Restricted to east Atlantic and Mediterranean; winters in strength off South Africa as discovered by van Oordt and Kruijt . Dispersed at sea when not breeding: adults pelagic mainly October–April. Degree of movement by Mediterranean breeders uncertain. Occurs in autumn in east Mediterranean, stragglers entering Black Sea and Sea of Azov in October; reported resident around Malta, and individuals ringed Filfla recovered nearby in January and in Tunisia in late December; no conclusive evidence of Mediterranean breeders emerging into Atlantic, but few winter records in Mediterranean. Marked southward migration by Atlantic breeders, though very small numbers (possibly late migrants) noted in north-temperate waters in early winter. Main departures from British and Irish waters September–November; migrants noted in Bay of Biscay and off Iberia up to December, though arrivals off west Africa from mid-November. Some occur in winter north to offshore Equatorial Guinea and Mauritania (Irish breeder recovered 19°N on 28 January); but most transequatorial migrants winter (December–April) in cool waters off South West and South Africa, some south to 38°S, 300 km south of Cape Agulhas. Dutch museums' winter specimens of juveniles all from west Africa, adults all South Africa. Scottish breeder recovered False Bay, Cape Town, February; another on south coast of Natal on late date of 2 May. Old reports from Zambesi mouth (Mozambique) and Red Sea unsubstantiated.
Substantial northward passage offshore from west Africa in March and April; April and May records from Cape seas and May ones in tropics probably mainly pre-breeders making more leisurely return towards colonies, which they visit after adults established there. Numerous recoveries demonstrating accuracy of return to colonies by adults; also many recorded inter-colony movements between those of English Channel, Wales and Ireland, and between Scotland and Faeroe Islands, mostly by presumed pre-breeders. Present far out to sea in north-east Atlantic in latitudes of colonies during breeding season as ‚off-duty‘ adults and non-breeders; infrequently found west of 20°W, but scattering of records out to 30°W, exceptionally to 40°W. One authentic North American record: Sable Island, off Nova Scotia, in August 1970; oft-quoted reports from Canada during 1882–1901 due to misidentifications. Small numbers occur in North Sea, and number obtained late in year at Danish lights. Inland only after storms, when recorded many European countries.
Thanks to Birds of the Western Palearctic